1. Field of the Invention
The present invention relates to a belt feeding device for use in an image forming apparatus such as an electrophotographic copying machine.
The belt feeding device is used as a device for feeding an image supporting body such as a belt-shaped photosensitive body or intermediate transfer body, or a device for feeding a sheet of paper in an image forming apparatus such as an electrophotographic copying machine.
2. Description of the Related Art
In such a belt feeding device as mentioned above, a crosswise position of a belt must be controlled in a predetermined range.
The following techniques are known as the related art for controlling the crosswise position of the belt.
(1) Technique shown in FIG. 14, or described in Japanese Utility Model Laid-open No. Sho 62-186180: PA0 (2) Technique shown in FIG. 15, or described in Japanese Utility Model Laid-open No. Sho 59-173059: PA0 (3) Technique shown in FIG. 16, or described in Japanese Patent Laid-open No. Sho 58-177811:
According to the method shown in FIG. 14, a pair of belt-shaped side stops 03 are formed at both end portions of the back surface of a belt 02 wrapped around a roll 01. The side stops 03 are guided by both ends of the roll 01 or grooves formed on the roll 01, thereby controlling the crosswise position of the belt 02. However, it is not easy to form the side stops 03 on the belt 02, causing an increase in cost. In case the belt 02 is frequently exchanged, this method is very uneconomical. In addition, the side stops 03 are prone to separate from the belt 02.
According to the method shown in FIG. 15, a pair of flanges 04 are formed on both ends of a roll 01, and both side edges of a belt 02 wrapped around the roll 01 are adapted to come into contact with the flanges 04, thereby controlling the crosswise position of the belt 02. Unlike the method shown in FIG. 14, no side stops are formed on the belt 02, so that the belt 02 can be simply made. However, since either side edge of the belt 02 comes into direct contact with the opposing flange 04, there is a possibility of occurrence of belt damage. Specifically, crosswise movement of the belt 02 is suppressed by either flange 04, causing axial slippage of the belt 02 on the roll 01. At this time, a load (edge force) applied between either side edge of the belt 02 and the opposing flange 04 is equal to a load of axial slippage of the belt 02 on the roll 01, whose value becomes tens of N (Newton). This load or edge force causes belt damage.
This edge force varies with the material of the belt 02. For example, when the material of the belt 02 is primarily composed of PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride), polycarbonate, or the like, an edge force of 15N or less provides a good result regarding the edge damage to the belt 02.
The method shown in FIG. 16 can solve the problem of the method shown in FIG. 15. That is, according to the method shown in FIG. 16, a roll 06 formed with a plurality of circumferential slits is used (this roll will be referred to also as Low Lateral Force roll or LLF roll for short). With the use of the LLF roll, the crosswise movement of the belt 02 can be absorbed without axial slippage on the roll 06 to thereby reduce an edge force applied to each of belt edge guide members 07 (edge guides). In this method, the edge force varies with form errors of crosswise movement factors such as parallelism of the roll 06 and other parallel rolls, cylindricity of the belt 02, and cylindricity of each roll. By suppressing the form errors of the crosswise movement factors to a certain level or less, the edge force can be stabilized to about 20N.
However, unless the crosswise movement factors are property set, a force (edge force) applied to each side edge of the belt 02 cannot be reduced to cause belt damage even by the technique using the LLF roll 06 shown in FIG. 16. In particular, an intermediate transfer belt using polycarbonate as the belt material is weak against load. If the belt is subjected to repeated load and sliding contact with the edge guides 07 due to the edge force, the belt becomes susceptible to belt damage such as wear, bend, or crack of each side edge. Further, in performing high-quality transfer with a paper feeding belt using PET (polyethylene terephthalate) or the like as the belt material, the thickness of the belt must be made small. Accordingly, the belt is similarly susceptible to belt damage.
When the belt damage occurs, the belt is conventionally exchanged. However, since frequent exchange of the belt is uneconomical, a belt feeding device less subjected to the belt damage has been demanded. Accordingly, a belt feeding device which can more reduce the edge force has been demanded. While the edge force can be reduced by reducing the form errors of the crosswise movement factors mentioned above, the reduction in the form errors is difficult to attain in a belt feeding device to be mass-produced. Furthermore, as the crosswise movement factors change in exchanging the belt, it is also difficult to maintain the value of the edge force less than 20N for a long time.
The less the edge force, the more desirable for the reduction in belt damage. However, no easy-to-adjust parameter for reducing the edge force has conventionally been known. Accordingly, the conventional belt feeding device with the edge force of about 20N is manufactured by increasing the axial uniformity of a roll diameter, the parallelism of roll shafts, etc. to some extent.
The present inventors have investigated to easily manufacture a belt feeding device which can reduce the edge force to about 15N or less. That is, the present inventors have investigated the parameter and the way of adjustment thereof to reduce the edge force applied to the belt of the belt feeding device to about 15N or less. As the result of investigation, it has been found that the edge force can be reduced to 15N or less by setting a load to an axial displacement of the belt wrapped around the rolls to 80 N/mm or less. Furthermore, it has been found that the setting of this load to the axial displacement of the belt to 80 N/mm or less can be easily attained by adjusting the form of the slits of the LLF roll. Thus, the present invention has been achieved in these circumstances.